In industries where large valves are employed, it has been common practice to utilize pneumatic wrenches, such as a nut runner tool, to rotate valve hand wheels to reduce the physical effort required to operate the valves. The wrenches are typically applied to the nut at the center of the hand wheel. A shortcoming of the use of such wrenches occurs when the valve comes to the limit of travel. The powerful rotational torque delivered by the pneumatic wrench is suddenly transmitted to the body of the person operating the tool. Such a sudden application of force transmitted to the body has become a cause of lost time injuries to plant personnel.
Various efforts have been undertaken to overcome this problem. In one application, a massive piping substructure was constructed about a valve. A pneumatic wrench was permanently affixed to the piping substructure to operate the valve. This system was very cost prohibitive and required a dedicated pneumatic wrench for each valve location. A second concept was the use of a forked reaction arm attached to the pneumatic wrench. The arm was placed over a plate and pipe bracket welded to the decking adjacent to the valve. Unfortunately, the piping system often undergoes large cycles of thermal expansion and contraction, with resulting movement relative to the bracket mounted to the stationary deck structure. Also, the forked arm was long and when torque loads were applied to the arm it spread the slot open, necessitating the periodic replacement of the forked arm. A third system was a plate and U-shaped strap bracket bolted to the valve itself just behind the hand wheel. The U-shaped strap bracket allowed the wrench to be cradled in the U-shaped strap.
Despite these efforts, a need still exists for an apparatus and method for the control of sudden applications of force by such power wrenches.